Abstract
Abd El-Rahman et al. (Flora Bd, 163:143–155, 1974) have shown that G. glabra grows under severe climatic conditions and adverse moisture supply and inhabits different types of soils. The amount of available soil moisture to the plant is a factor of paramount importance in the plant life in arid zones, which varies in different localities supporting the plant. He studied it after planning to cultivate some economic plants in desert and semidesert areas in Egypt. It seems necessary to study the water relations of these plants including G. glabra. Their investigation deals with the water relations of this plant, comprising studies on the transpiration, osmotic pressure and water saturation deficit in two localities, namely Burg El Arab and Wadi El Natrun in Egypt. The first is a locality in the Western Mediterranean coastal region and the second represents a site on the escarpment bordering Wadi El Natrun depression in the Lybian desert (Abd El-Rahman et al. in Flora Bd, 163:143–155, 1974). They conducted transpiration measurements which show that the plant transpires at relatively higher rates than desert plants. The curves of diurnal march of the transpiration and those of the stomatal aperture showed almost the same trend, indicating a strong stomatal control on transpiration. The plant exhibits high values of osmotic pressure and water saturation deficit which increase by the progress of the growing season. These values are higher in the locality with relatively low available soil moisture. The plant has been found to withstand high water deficits for long periods.